1. Field of the Invention
The present invention is directed to low surface energy polyisocyanates which contain allophanate groups, isocyanurate groups and fluorine, to a process for their preparation by
a) trimerizing the isocyanate groups of organic diisocyanates in the presence of alcohols containing fluorine, and to their use in one- and two-component coating compositions. PA0 i) having an NCO content of 5 to 35% by weight and prepared from an organic diisocyanate, PA0 ii) containing at least 1% by weight of isocyanurate groups (calculated as N.sub.3,C.sub.3,O.sub.3, MW 126), PA0 iii) containing allophanate groups in an amount such that there are more equivalents of allophanate groups than urethane groups and PA0 iv) containing fluorine (calculated as F, AW 19) in an amount of 0.001 to 50% by weight, PA0 i) having an NCO content of 5 to 35% by weight and prepared from an organic diisocyanate, PA0 ii) containing at least 1% by weight of isocyanurate groups (calculated as N.sub.3,C.sub.3,O.sub.3, MW 126), PA0 iii) containing allophanate groups in an amount such that there are more equivalents of allophanate groups than urethane groups and PA0 iv) containing fluorine (calculated as F, AW 19) in an amount of 0.001 to 50% by weight, PA0 b) adding 0.01 to 500 millimoles, per mole of organic diisocyanate, of a compound containing two or more carbon atoms, one or more hydroxyl groups and one or more fluorine atoms to the organic diisocyanate prior to or during step a) and optionally a non-fluorine-containing monoalcohol, PA0 c) converting a sufficient amount of the urethane groups formed from the reaction of isocyanate groups with the compounds added in step b) to allophanate groups such that there are more equivalents of allophanate groups than urethane groups, PA0 d) terminating the trimerization reaction at the desired degree of trimerization by adding a catalyst poison and/or by thermally deactivating the catalyst and PA0 e) optionally removing unreacted organic diisocyanate.
2. Description of the Prior Art
Polyurethane coating compositions containing a polyisocyanate component, in either blocked or unblocked form and an isocyanate-reactive component, generally a high molecular weight polyol, are well known.
Although coatings prepared from these compositions possess many valuable properties, one property, in particular, which needs to be improved is the surface quality. It can be difficult to formulate coating compositions to obtain a coating having a smooth surface as opposed to one containing surface defects such as craters, etc.
It is believed that these difficulties are related to the high surface tension of the two-component coating compositions. Another problem caused by the high surface tension is the difficulty in cleaning the coatings. Regardless of their potential application area, there is a high likelihood that the coatings will be subjected to stains, graffiti, etc.
Accordingly, it is an object of the present invention to provide coating compositions which have reduced surface tension and, thus, are suitable for the production of coatings having an improved surface. It is an additional object of the present invention to provide coating compositions which have improved cleanability. It is a final object of the present invention to provide coating compositions which satisfy these requirements without substantially affecting the other valuable properties of the known polyurethane coatings.
Surprisingly, these objectives may be achieved by formulating coating compositions with the polyisocyanates according to the present invention containing allophanate groups, isocyanurate groups and fluorine which are described hereinafter.